1. Field of the Invention
This invention relates generally to flexible couplings and, more particularly, to an improved flexible coupling for transmitting torque from a driving member to a driven member.
2. Description of the Prior Art
A flexible high speed coupling shaft is often employed in conjunction with a propulsion system to transmit shaft torque to a load. For example, such a shaft may be employed in conjunction with the power turbine of a marine or industrial gas turbine engine to transmit torque such as to a ship's propeller reduction gearing or to the impeller shaft of a pump. A flexible high speed coupling shaft is advantageous in such instances because it compensates for axial, parallel offset and angular propulsion system/reduction gear positioning misalignments while transmitting the shaft torque to the load and limiting the axial load to be compatible with the anti-friction thrust bearings.
One such prior art flexible high speed coupling shaft which is currently utilized in conjunction with a marine gas turbine propulsion system is comprised of a distance piece supported at its forward or driving end by a dual disc flexible coupling which is attached to a driving member. The aft or driven end of the distance piece is supported by a second dual disc flexible coupling which, in turn, is attached to a driven member. A piston ring damper assembly is connected to the aft flexible coupling to dampen axial deflections and antideflection rings are positioned circumferentially about each of the couplings to limit deflections due to radial impact loads. The axial resonance frequency of such a flexible high speed coupling shaft spring/mass system is a function of the coupling axial spring rates and the coupling supported weight of the distance piece and is generally in the 18 to 25 Hz range.
Although the above-described flexible high speed coupling shaft performs satisfactorily with current ocean-going vessels, it was found to be unacceptable for use in vessels designed to operate primarily in shallow waters. Such shallow water vessels generally have smaller diameter propellers with higher screw-turning speeds than those of the ocean-going vessels. The smaller, faster propellers result in blade passing frequencies which approach and fall within the critical axial resonance frequency range of the prior art flexible high speed coupling shaft spring/mass system. In addition, it was found that the prior art piston ring axial deflection damper assembly is subjected to wear, which may eventually cause it to become ineffective.
It is, therefore, an object of the present invention to provide an improved flexible coupling which raises the axial resonance frequency of a flexible high speed coupling shaft.
It is a further object of the present invention to provide such a flexible coupling which maintains a high degree of torque carrying and alignment offset capability.
It is another object of the present invention to provide such a flexible coupling which eliminates the need for an axial deflection damper assembly.
It is yet another object of the present invention to provide such a flexible coupling which includes a radial snubber feature to limit radial deflections of the shaft.